midiapplet.java

java2编程21天自学通中的源码

import javax.swing.*;
import java.awt.event.*;
import javax.sound.midi.*;
import java.awt.GridLayout;
import java.io.File;

public class MidiApplet extends javax.swing.JApplet {
    public void init() {
        JPanel pane = new JPanel();
        MidiPlayer midi = new MidiPlayer(getParameter("file"));
        pane.add(midi);
        setContentPane(pane);
    }
}

class MidiPlayer extends JPanel implements Runnable, ActionListener {

    Thread runner;
    JButton play = new JButton("Play");
    JButton stop = new JButton("Stop");
    JLabel message = new JLabel();
    JComboBox tempoBox = new JComboBox();
    float tempo = 1.0F;
    Sequence currentSound;
    Sequencer player;
    String songFile;

    MidiPlayer(String song) {
        super();
        songFile = song;
        play.addActionListener(this);
        stop.setEnabled(false);
        stop.addActionListener(this);
        for (float i = 0.25F; i < 7F; i += 0.25F)
            tempoBox.addItem("" + i);
        tempoBox.setSelectedItem("1.0");
        tempoBox.setEnabled(false);
        tempoBox.addActionListener(this);
        setLayout(new GridLayout(2, 1));
        add(message);
        JPanel buttons = new JPanel();
        JLabel tempoLabel = new JLabel("Tempo: ");
        buttons.add(play);
        buttons.add(stop);
        buttons.add(tempoLabel);
        buttons.add(tempoBox);
        add(buttons);
        if (songFile == null) {
            play.setEnabled(false);
        }
     }

    public void actionPerformed(ActionEvent evt) {
        if (evt.getSource() instanceof JButton) {
            if (evt.getSource() == play)
                play();
            else
                stop();
        } else {
            String item = (String)tempoBox.getSelectedItem();
            try {
                tempo = Float.parseFloat(item);
                player.setTempoFactor(tempo);
                message.setText("Playing " + songFile + " at "
                    + tempo + " tempo");
            } catch (NumberFormatException ex) {
                message.setText(ex.toString());
            }
        }
    }

    void play() {
        if (runner == null) {
            runner = new Thread(this);
            runner.start();
            play.setEnabled(false);
            stop.setEnabled(true);
            tempoBox.setEnabled(true);
        }
    }

    void stop() {
        if (runner != null) {
            runner = null;
            stop.setEnabled(false);
            play.setEnabled(true);
            tempoBox.setEnabled(false);
        }
    }

    public void run() {
        try {
            File song = new File(songFile);
            currentSound = MidiSystem.getSequence(song);
            player = MidiSystem.getSequencer();
        } catch (Exception ex) {
            message.setText(ex.toString());
        }
        Thread thisThread = Thread.currentThread();
        while (runner == thisThread) {
            try {
                player.open();
                player.setSequence(currentSound);
                player.setTempoFactor(tempo);
                player.start();
                message.setText("Playing " + songFile + " at "
                    + tempo + " tempo");
                while (player.isRunning() && runner != null) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) { }
                }
                message.setText("");
                player.close();
            } catch (Exception ex) {
                message.setText(ex.toString());
                break;
            }
        }
    }
}